International travel poses multiple challenges to the control of HIV in the US and worldwide. US residents may acquire HIV abroad and introduce transmission into local networks not previously affected. HIV-positive US residents may transmit HIV infection to others while traveling. The high level of antiretroviral (ARV) treatment in the US raises the specter of spreading ARV drug resistance worldwide, an outcome particularly worrisome to developing countries with limited second-line treatment options. HIV transmission risk may be compounded in foreign settings by destination-specific information, differing motivation, and additional behavioral skills that are necessary for risk reduction behaviors while traveling internationally. The community of men who have sex with men (MSM) in San Francisco represents a population with a high degree of international travel, along with a high prevalence of HIV, a high level of ARV treatment, and a high level of ARV drug resistance. Our study proposes to measure risk of HIV acquisition and transmission in the population of MSM who travel internationally in San Francisco. The specific aims: 1) to measure the prevalence of sexual risk behavior during international travel; 2) to document the potential for ARV drug resistance transmission through international travel; and 3) to examine the informational, motivational, and behavioral skills correlates of safer sex disinhibition during international travel. Our study will assess sexual risk behavior and potential correlates of behavioral disinhibition, organized according to the Information-Motivation-Behavioral Skills (1MB) model of HIV behavior change. We will use Respondent-Driven Sampling (RDS) to recruit a representative cross-sectional survey of 1500 MSM in San Francisco who have traveled internationally in the past 12 months. We will obtain population-based estimates of unprotected anal intercourse and ARV drug resistance prevalence (Aims 1 and 2). HIV risk behavior data will be obtained using questionnaires specifically designed to collect detailed data on both the individual and destination-specific informational, motivational, and behavioral skills components that may affect safer sex disinhibition while traveling internationally (Aims 1,2, and 3). Public health relevance: Our study design will provide data on individual characteristics that may influence HIV risk behavior across situations, as well as destination-specific attributes that specifically influence behavior while visiting a particular location. Ultimately, our study will contribute to the development of prevention strategies specifically addressing the correlates of behavioral disinhibition associated with cross- border HIV transmission and spread of ARV drug resistance in an era of expanding treatment worldwide. [unreadable] [unreadable] [unreadable]